Semi-conductor unit



NOV.,18, 1958 H SEMI-CONDUCTOR UNIT Filed May 29. 1953 United StatesPatent G F SEMI-CONDUCTOR UNIT Gerald C. Rich, Scottsdale, Ariz.,assignor to Motorola, Inc., Chicago, 111., a corporation of IllinoisApplication May 29, 1953, Serial No. 358,241 12 Claims. (Cl. 317-235Patented Nov. 18, 1958 Another feature of the invention is the provisionof such a circuit element in which pads are also provided on the discadjacent the metallic coatings to assure proper contact of the line ofjuncture of the crystal with the metallic deposits.

Yet another feature of the invention is the provision of an'improvedprocess whereby the emitter and collector electrodes of a transistor areobtained by photo engraving with precise minute dimensions and accurateminute spacing.

A further feature of the invention is the provision of such a transistorunit in which the aforesaid insulating disc and transistor are supportedand aligned in a simple unitary casing in such a manner that the unitmay be easily assembled, and is rugged and exhibits a high degree ofmechanical stability.

The above and other features of the invention which are believed to benew are set forth with particularity in the block or tab is alsoprovided and aflixed to another surface of the crystal to constitutewhat is termed a base electrode for the assembly.

' The emitter and collectorelectrodes in the prior art point contacttransistor usually take the form of a pair of fine wires or thinmetallic ribbons. These wires are supported by the transistor casing toextend perpendicularly to a surface of the crystal with pointed ends inpoint contact with that surface. These wires have a diameter of theorder of .002" and their points are spaced about .002" on the face of acrystal having cubical dimensions of the order of .032 on a side. Suchelectrodes require a high degree of manual dexterity in their assemblyto mountand achieve proper placement thereof due to their microscopicsize and spacing. Since these prior art as semblies require visualadjustment and a high degree of manual proficiency, their constructionis complicated and expensive and it is difficult to maintain uniformityin the product when the units are fabricated on a mass production basis.

It is an object of the present invention to provide an improved pointcontact type transistor assembly in which the collectorand emitterelectrodes are fabricated in a simplified manner by mechanical ratherthan manual techniques for accurate dimensioning and positioning of theelectrodes.

A further object of the invention is to provide such an improvedtransistor unit that may be produced on a mass production basis andwhich is constructed so that units so produced have uniformcharacteristics and are not subject to variations from one unit to thenext.

Another object of the invention is to provide such an improvedtransistor unit that may be produced at a low cost and yet in which thevarious components are precisely positioned and have a high degree ofmechanical stability.

A still further object of the invention is to provide an improvedprocess for obtaining precisely spaced point contact electrodes in atransistor of relatively small size.

A feature of the invention is the provision of a circuit element in theform of a transistorunit in which the emitter and collector electrodesare thin, precisely spaced, metallic coatings on an insulating disc, andin which the disc is placed over the line of juncture between twoinclined faces of a semi-conductive crystal with the aforementionedmetallic coatings traversing the line of junc ture at spaced pointsalong the line and in point contact therewith. 7

appended claims. The invention itself, however, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description when taken in conjunction with theaccompanying drawing in which:

Figure 1 shows a complete transistor assembly constructed in accordancewith the invention;

Figure 2 shows a component of the improved transistor unit of theinvention;

Figure 3 shows a complete transistor unit constructed in accordance witha modification of the invention; and

Figure 4 shows a component of the modification of Figure 3.

The present invention is directed to a transistor element whichcomprises a block of semi-conductive material having a pair of inclinedfaces forming a line of juncture therebetween. A supporting member isprovided having a surface facing the aforesaid line of juncture, and apair of metallic coatings is disposed on the aforementioned surface ofthe supporting member. The metallic coatings are mutually displaced andinsulated one from the other, and these coatings traverse and contactthe aforesaid line of juncture at spaced points along such line.

Referring now to Figures 1 and 2, one transistor unit of the inventioncomprises a casing in the form of a metallic cylinder 10 which has asuitable shape to support a disc-like insulating base 11 at one end anda disclike insulating member or button 12 at the other. Asemi-conductive crystal 13, such as a germanium crystal, is supportedwithin the casing between members 11 and 12 by means of a resilientspring 14. The crystal has a pair of inclined faces 15, 16 with a lineof juncture 17 therebetween, and resilient spring 14 urges the line ofjuncture 17 upwardly against the surface of member 12 facing such lineof juncture. The interior of the metallic cylinder 10 which containscrystal 15 is preferably filled with a potting compound.

Base 11 has a notch 18 formed in its periphery which mates with acorresponding deformed section of cylinder 10 for aligning purposes.Disc 12 has a similar notch formed in its periphery which mates with aprotrusion in cylinder 10 for the same reason.

The resilient spring 14 not only resiliently biases the crystal againstthe lower surface of disc 12, but also forms a contact to the baseelectrode of crystal 13. The base electrode is formed by the upper end14a of the spring which is afiiXed to the'crystal.

As shown in Figure 2, the surface of disc 12 facing the aforesaid lineof juncture 17 of crystal 13 has a pair of bar-shaped metallic elements19, 20 formed thereon in mutually spaced parallel relation and insulatedone from the other. The metallic elements 19 and 20v are so positionedthat when member 12 is assembled in the transistor unit, these elementstraverse the aforesaid line of juncture 17 of crystal 13 and contact thecrystal at spaced points along the line of juncture. In this manner,metallic elements 19 and 20 respectively form the collector and emitterelectrodes for the transistor, and electrical connection is made tothese respective elements by wire leads 21, 22 extending through disc12. Disc 12 also has a pair of apertures 23, 24 therein through whichthe aforementioned potting compound may be introduced into the interiorof the transistor unit. 7

In accordance with one aspect of the invention, elements 19 and 20' areformed on insulating disc 12 by a photo-engraving technique; The dischas a diameter of the order of .250" and it is desirable that theelements 19 and 20 be about .0005 wide and separated by .001 or less.The use of photo-engraving allows the ele ments to be drawn aboutfifteen times normal sizeand a negative made of the drawing. Thenegative then may be reduced to the actual size of the disc and elementswith all dimensions precisely and rigidly retained.

One process by which elements 19 and 20 may be formed on disc 12 is asfollows. A board is provided having a copper coating of, for example,1.0 mil on at least one surface. Copper clad insulating boards areobtainable commercially and the discs can be formed in quantities fromsuch boards. The copper-clad board is first cleaned with pumice andwashed. The board is further cleaned with muratic acid and salt. Anonorganic photo-sensitive resist is then applied over the coppersurface of the board. This resist may, for example, be composed ofpolyvinylalcohol. The resist is dried by spinning the board atapproximately 55 R. P. M. over a sink with the coated surface facingdownwardly, and then spinning the board over a hot plate for about twominutes. A contact print is made by exposing the portions of the resistcorresponding to elements 19 and 20 through an appropriate negative forabout two minutes about 7 /2 from a 275 watt sun lamp. The negative ismade by photographing an enlarged drawing of the elements and reducingthe photograph to the minute dimensions desired. The resist is thendeveloped by water under a faucet for thirty sections, and the exposedportions of the resist are hardened by immersing the board in a solutionof four ounces of chromic acid and one ounce of Duponul in one gallon ofwater. The board is then rinsed and heated to 400 on a hot plate. Theunexposed resist is then removed by a solution of one ounce of muraticacid and a pinch of salt in a pint of water. The copper surface of theboard uncovered by the removal of the unexposed resist is etched away bya ferric chloride anhydrous (FeCl solution. The exposed resist is thenremoved in any known manner leaving the elements 19 and 20 bonded to theboard. The desired shaped disc 12 is then punched from the board.

In this manner, the two elements '19 and 20 are formed on the extremelysmall disc, these elements having accurate minute dimensions andspacing. These assemblies can be conveniently mass produced, each beingheld to close tolerances for uniform characteristics in the resultingtransistor units.

Base 11 may similarly be coated with a copper or other metallic layer 25bonded to its upper surface to facilitate electrical connection toresilient spring 14 and, thence, to base electrode 14a. Spring 14 (andits end 14a forming the base electrode) may be composed, for example, ofPhosphor bronze or beryllium copper which exhibits the desiredelectrical and resilient characteristics. The bottom of spring is issoldered to a coating 25, and the coating makes electrical contact withmetallic cylinder so that the cylindrical casing itself is connected tothe base electrode 14a of crystal 13 and suitable electrical connectioncan be made to the casing to complete the transistor circuit.

The following dimensions are given for the transistor unit of theinvention merely by Way of example and are not intended to limit theinvention in any way.

. Inches Diameter of cylinder 10 .250 Height of cylinder 10 .300Thickness of cylinder walls .005 Thickness of discs 11 and 12 .065

Width of metallic elements 19, 20 .0005 Separation of metallic elements19, 20 .00l Length of metallic elements 19, 20 .100

The embodiment of the invention shown in Figures 3 and 4 is similar inmany respects to that of Figures 1 and 2 and like elements have beenindicated by like numerals. In the latter embodiment, a conical shapedresilient coil spring 50 is used to urge crystal 13 against the bottomsurface of disc 12, and spring 50 constitutes a base electrode for thecrystal and a connection thereto from the coating 25 on disc 11. A lead51 is soldered or otherwise afiixed to coating 25 and extends through anaperture 52 in disc 12 to constitute a connection to the base electrode.7

Metallic elements 19 and 20 have enlarged area portions 19a and 20aadjacent their respective connections to leads 21 and 22 to increasethis current carrying and heat dissipating capacity. Moreover, a pair ofpads 53 and 54 is provided on each side of elements 19 and 20 andspaced, for example, .020" from the respective elements and parallelthereto. These pads may be in the form of copper bars deposited on disc12 during the deposition of elements 19 and 20. The purpose of the padsis to maintain the edge 17 of the crystal across the elements andprevent that edge from tilting and contacting only one of the elements.That is, these pads provide an electrically isolated, but mechanicallyintegrated, cushion which implements uniform contact of the edge of thecrystal with elements 19 and 20. The pads 53 and 54 also reduce anytendency of the edge of the crystal to slide along elements 19 and 20due to the increased friction supplied thereby.

The invention provides, therefore, a transistor unit which is capable ofbeing produced in large quantities, and which is so constructed that thetransistor units so produced exhibit uniform characteristics from oneunit to another. This is achieved since the collector and emitterelectrodes 19 and 20 may be formed mechanically to have precisedimensions without need for manual skill in the placement of theseelectrodes as is the case when fine wires are used. Moreover thetransistor unit of the invention may be assembled easily and cheaplysince each and every component thereof may be manufactured mechanicallyand assembled with a high degree of facility.

The transistor unit of the invention utilizes relatively inexpensivecomponent parts and, as mentioned above, may be assembled simply andeconomically, and this results in a finished unit of relatively lowcost. In addition, the transistor unit of the invention has a highdegree of mechanical stability and is small in size.

While particular embodiments of the invention have been shown anddescribed, modifications may be made and it is intended in the appendedclaims to cover all such modifications as fall within the true spiritand scope of the invention.

I claim:

1. A transistor unit including in combination, a semiconductive crystalhaving a pair of inclined faces forming a line of juncture therebetween,an insulating panel disposed parallel to the aforesaid line of junctureand having a flat surface facing such line, and a pair of etched thinelongated metallic means on the aforesaid surface of said insulatingpanel in spaced parallel relation and insulated one from the other, andmeans for resiliently maintaining said semi-conductive crystal incontact with each of said pair of etched thin elongated metallic means.'2 A transistor unit including in combination, a semi conductive crystalunit having a pair of inclined faces forming a line of juncturetherebetween, a cylindricalshaped casing, a disc-like insulating membersupported in said casing parallel to the aforesaid line of juncture andhaving a fiat surface facing such line, a pair of thin elongatedmetallic coatings bonded to the aforesaid surface of said insulatingmember in mutually spaced, parallel relation and insulated one from theother, said metallic coatings traversing the aforesaid line of juncture,a disc-like base member supported in said casing parallel to said firstmentioned disc-like member with said crystal unit disposed between saiddisc like members, and a resilient spring means connected to saidcrystal unit and to said disc-like base member for urging said crystalunit against the aforesaid surface of said disc-like insulating memberso that said metallic coatings contact the aforesaid line of juncture atspaced points along said line.

3. A transistor unit including in combination, a semiconductive crystalhaving a pair of inclined faces forming a line of juncture therebetween,a tubular-shaped casing, a disc-shaped insulating panel supported insaid casing parallel to the aforesaid line of juncture and having asurface facing such line, a pair of thin elongated metallic coatingsbonded to the aforesaid surface of said insulating panel in mutuallyspaced, parallel relation and insulated one from the other, saidmetallic coatings traversing the aforesaid line of juncture, a disc-likeinsulating base panel supported in said casing parallel to said firstmentioned disc-like panel with said crystal disposed between saidpanels, a metallic coating bonded to the surface of said base panelfacing said crystal, and a resilient spring connected to said crystaland to said base panel to constitute an electrode for said crystal andto bias said crystal against the aforesaid surface of said firstmentioned disc-like insulating panel so that said metallic coatingscontact the aforesaid line of juncture at spaced points along said line.4. A transistor unit including in combination, a semiconductive crystalhaving a pair of inclined faces forming a line of juncture therebetween,a tubular-shaped casing having internal aligning protuberances, adisc-shaped insulating panel supported in said casing parallel to theaforesaid line of juncture and having a surface facing such line, saidpanel also having a peripheral aligning notch therein engaging one ofthe aforesaid protuberances of said casing, a pair of thin elongatedmetallic coatings bonded to the aforesaid surface of said insulatingpanel in mutually spaced, parallel relation and insulated one from theother, said metallic coatings traversing the aforesaid line of juncture,a disc-like insulating base panel supported in said casing parallel tosaid first mentioned disc-like panel with said crystal disposed betweensaid panels, said base panel having a peripheral aligning notch thereinengaging one of the aforesaid protuberances of said casing, a metalliccoating bonded to the surface of said base panel facing said crystal, aresilient spring connected to said crystal and to said base panel toconstitute an electrode for said crystal and to bias said crystalagainst the aforesaid surface of said first mentioned insulating panelso that said metallic coatings contact the aforesaid line of juncture atspaced points along said line, and potting compound completely fillingsaid casing.

5. A circuit element including in combination, a block ofsemi-conductive material having a pair of inclined faces forming a lineof juncture therebetween, a supporting member having a surface facingthe aforesaid line of juncture, at least one electrically conductiveelement disposed on the aforesaid surface of said supporting member,said metallic element traversing the aforesaid line of juncture and incontact therewith, and at least one pad disposed on the aforesaidsurface adjacent said electrically conductive element for assuringcontact of the aforesaid line of juncture with said element.

6. A circuit element including in combination, a block ofsemi-conductive material having a pair of inclined faces forming a lineof juncture therebetween, an insulating supporting member having a flatsurface facing the aforesaid line of juncture, a pair of elongatedmetallic elements disposed on the aforesaid surface of said insulatingsupporting member in spaced parallel relation, said metallic elementstraversing and contacting the aforesaid line of juncture at spacedpoints along said line, and a pair of pads disposed on the aforesaidsurface of said supporting member adjacent said metallic elements oneach side thereof for assuring contact of the aforesaid line of juncturewith each of said metallic elements.

7. A circuit element including in combination, a block ofsemi-conductive material having a pair of inclined faces forming a lineofjuncture therebetween, an insulating supporting member having a'flatsurface facing the aforesaid line of juncture, a pair of elongatedmetallic elements formed on the aforesaid surface of said insulatingsupporting member in spaced parallel relation, said metallic elements.traversing and contacting the aforesaid line of juncture at spacedpoints along said line, and a pair of elongated metallic pads formed onthe aforesaid surface of said supporting member adjacent said metallicelements and parallel thereto on each side of said metallic elements,said pads assuring contact of the aforesaid line of juncture with eachof said metallic elements.

8. A method for producing a semi-conductive unit which comprises,providing a flat insulating supporting member, obtaining an enlargedrepresentation of a pair of electrically conductive elements to bedisposed on a surface of said supporting member, said representationhaving dimensions substantially larger than the dimensions of saidsupporting member, obtaining a photographic negative of saidrepresentation having dimensions reduced to correspond to those of saidsupporting member, utilizing said negative to dispose a pair of spacedelectrically conductive elements on said supporting member, providing ablock of semi-conductive material having a pair of inclined facesforming a line of juncture therebetween, and supporting said block withits line of juncture facing said surface of said supporting membertraversing said pair of electrically conductive elements and in contacttherewith.

9. A method for producing a transistor which comprises, providing a flatinsulating supporting disc having a diameter of the order of .250",obtaining an enlarged representation of a pair of electricallyconductive elements to be disposed on a surface of said disc, saidrepresentation having dimensions substantially larger than the diameterof said disc, obtaining a photographic negative of said representationhaving dimensions reduced to correspond to those of said disc, andutilizing said negative to dispose a pair of electrically conductiveelements on said disc each having a length of the order of .100", awidth of the order of .0005,'and spaced one from the other to the orderof .001" and providing a single semi-conductor element in engagementwith said pair of electrically conductive elements.

10. A method for producing a semi-conductor device which comprises,providing a fiat metal member, obtaining an enlarged representation of apair of electrically conductive elements to be disposed on the surfaceof said metal member, obtaining a photographic negative of saidrepresentation, utilizing said negative to provide a pair of spacedelectrically conductive elements from said metal member, providing asemi-conductor element in contact with said pair of spaced electricallyconductive elements, and providing supporting and encasing means forsaid semi-conductor device.

11. A method for producing a semi-conductive device which comprises,providing a supporting member, providing a flat metallic layer thereon,obtaining an enlarged representation of a pair of electricallyconductive ele ments, obtaining a photographic negative of saidrepresentation having dimensions reduced to a desired value,

and using said negative to form a pair of spaced electrically conductiveelements in saidmetallic layer on said supporting member, providing aunit of semiconductive material with a contact edge thereon, andsupporting said unit on said device with said contact edge traversingsaid pair of electrically conductive elements and in engagementtherewith.

12. In a semi-conductor device which is small in size and must beassembled in precision fashion, the combination with a semi-conductorelement supported within an enclosing housing, contact leads extendingout of said housing, and means supported within said housing forelectrical connection with said contact leads and with saidsemi-conductor element, said means comprising a pair of etched metalelectrodes originally laid out in large size and brought down to a verymuch smaller size by photographic process for use in the device, witheach of said pair of etched metal electrodes being in electricalconnection with a corresponding one of said contact leads.

References Cited in the file of this patent UNITED STATES PATENTS924,827 Pickard June 15, 1909 2,413,186 LaRue Dec. 24, 1946 2,441,591)Ohl May 18, 1948 2,584,461 James et al. Feb. 5, 1952 2,597,734 Iaines ctal. May 20, 1 952 2,609,427 Stelmak Sept. 2, 1952 2,618,690 StuetzerNov. 18, 1952

